In recent years, with the development of electronic information technology, electronic equipments have become miniaturization, high-density, and information trends to be large-capacity and high-speed, which put forward higher requirements for overall performance of circuit substrates including heat resistance, water absorption, chemical resistance, mechanical properties, dimensional stability, dielectric properties and others.
In terms of dielectric properties, the relationship between signal transmission rate and dielectric constant Dk of insulating material in high-speed circuit is that: the lower the dielectric constant Dk of insulating material is, the faster the signal transmission rate is. Therefore, to achieve high signal transmission rate, substrates having low dielectric constant must be developed. As the signal rate becoming high, the loss of signal in the substrate can no longer be ignored. The relationship among signal loss and rate, dielectric constant Dk and dielectric loss factor Df is that: the smaller the dielectric constant Dk of a substrate is, the smaller the dielectric loss factor Df is, and the smaller the signal loss is.
Therefore, the development of a high-speed circuit substrate having low dielectric constant Dk, low dielectric loss factor Df and good heat resistance becomes a research direction commonly focused by CCL manufacturers.
Polyphenylene ether resin contains a large number of benzene ring structures in its molecular structure, and no strong polar group, giving excellent performances to polyphenylene ether resin, such as high glass transition temperature, good dimensional stability, low linear expansion coefficient and low water absorption, especially excellent low dielectric constant and low dielectric loss, and thus is an ideal resin material for preparing high-speed circuit boards.
Butadiene-styrene copolymer does not contain polar groups, and has good dielectric properties, low water absorption, good flexibility. Butadiene-styrene copolymer contains reactive vinyl group and is commonly used as a crosslinking agent for high-speed electronic circuit substrate resin systems.
Maleimide has excellent heat resistance, flame resistance, mechanical properties and dimensional stability, and is usually used as a crosslinking agent for high-speed electronic circuit substrate resin systems.
CN103965606A discloses a low dielectric material comprising: 40 to 80 parts by weight of polyphenylene ether, 5 to 30 parts by weight of bismaleimide, and 5 to 30 parts by weight of a polymer additive. Wherein the structural formula of the polyphenylene ether is as follow:
the polymer additive is selected from the group consisting of polybutadiene, styrene-butadiene copolymer, styrene-butadiene-divinylbenzene copolymer, styrene-maleic anhydride copolymer, maleic anhydride-grafted polybutadiene, and combinations thereof. Since styrene-butadiene copolymer, polybutadiene, styrene-butadiene copolymer-divinylbenzene copolymer and polyphenylene ether are incompatible with maleimide, there are problems in the mixing process that: glue liquid is layered, the surface of prepreg has turtle-like cracks, and substrate resin area has a phase separation.
CN101643650A discloses a phosphorus-containing flame retardant for use in an electronic circuit substrate. The phosphorus-containing flame retardant is added to resin systems having unsaturated double bonds, engineering plastics or polyolefin polymers, and plays roles of crosslinking and flame retardancy. Wherein, the resin having unsaturated double bonds includes homopolymers or copolymers of butadiene, styrene, isoprene, divinylbenzene, methylstyrene, acrylate, acrylonitrile, N-phenylmaleimide, N-vinylphenylmaleimide; vinyl substituted polyphenylene ethers; for example, a resin composition of a copolymer of butadiene, styrene and N-phenylmaleimide and a vinyl-substituted polyphenylene ether, or a resin composition of a copolymer of butadiene, styrene and N-vinylphenylmaleimide and a vinyl-substituted polyphenylene ether is used for preparing electronic circuit substrates. Since the used maleimide has a monomaleimide structure, the prepared substrate has lower heat resistance, higher thermal expansion coefficient, shorter thermal stratification time and lower thermal decomposition temperature, compared with a substrate prepared using maleimide having a bifunctional maleimide or polyfunctional maleimide structure.
CN101370866A discloses a resin composition which is a thermosetting resin composition of a semi-IPN type composite. Wherein, the resin composition is derived from a semi-cured resin composition formed by compatibilizing a prepolymer of butadiene polymer and a crosslinking agent with polyphenylene ether. Wherein, the butadiene polymer contains 40% or more of a 1,2-butadiene unit having a 1,2-vinyl group in a side chain in the molecule and is not chemically modified. In this invention, the polyphenylene ether is a thermoplastic high molecular polymer, and the molecular weight thereof is preferably 7,000-30,000. As can be seen from the examples, thermoplastic polyphenylene ether from Asahi Kasei Chemicals Corporation, Japan, in the tradename of S202A was used. Since the thermoplastic polyphenylene ether was incompatible with the butadiene polymer, the thermoplastic polyphenylene ether and the butadiene polymer were compatibilized in order to improve the compatibility between them. Since crosslinking reaction cannot occur between the thermoplastic polyphenylene ether and the butadiene polymer, a crosslinking agent (e.g. maleimide) is introduced to crosslink the butadiene polymer. Prepolymer of the butadiene polymer and the crosslinking agent was compatibilized with polyphenylene ether, and thus an uncured semi-IPN homogeneous composite thermosetting resin composition of polyphenylene ether-modified butadiene polymer was obtained. It is conceived that homogenization (compatibilization) in this case is not related to forming chemical bonds between polyphenylene ether and the other component (prepolymer of the butadiene polymer and the crosslinking agent), but is related to microphase separation resulting from physical mutual entanglement of molecular chains of polyphenylene ether and the other component (prepolymer of the butadiene polymer and the crosslinking agent). Therefore, it is conceived that the resin composition is apparently homogenized (compatibilized). The structure of the IPN type homogenous composite thermosetting resin composition has a structure as shown in the FIGURE.
Since this invention employs thermoplastic polyphenylene ether and butadiene polymer, there are problems as follows:
(1) Since the thermoplastic polyphenylene ether has a high molecular weight (the thermoplastic polyphenylene ether which is used in the examples and is the only one used is a thermoplastic polyphenylene oxide S202A from Asahi Kasei Chemicals Corporation, Japan and has a number average molecular weight of 16,000), the prepared glue has a high viscosity and the prepared prepreg has a poor appearance (with stripes, colloidal particles, dry flowers, bubbles);(2) Since the used thermoplastic polyphenylene ether does not contain vinyl active functional group, it cannot be crosslinked and cured with butadiene polymer. Therefore, compared with the thermosetting modified polyphenylene ether comprising vinyl, the used thermoplastic polyphenylene ether has worse heat resistance, resulting in insufficient heat resistance of the prepared electronic circuit substrate, and thus the prepared PCB used for high multi-layer high-speed electronic circuit has a significant heat resistance problem that delamination will occur after several harsh lead-free reflow solderings.
WO2013/110068A1 discloses a resin composition comprising: from 30 to 80 wt % of a resin, a base resin prepolymer, and combinations thereof; from 1 to 30 wt % of at least one monomer of mono maleimide, bismaleimide or a combination of mono maleimide and bismaleimide monomers; a flame retardant; and an initiator. In this invention, the resin prepolymer refers to a prepolymer of polyolefin resin and maleimide resin. Polyolefin resin includes polybutadiene, styrene-butadiene copolymer, polyisoprene, styrene-butadiene-divinylbenzene copolymer. Maleimide includes mono maleimide, bismaleimide or a combination of mono maleimide and bismaleimide monomers. As can be seen from the description of this invention, the resin composition further comprises polyphenylene ether, of which the molecular chain end structure is phenylhydroxy, methacrylate or acrylate group. Polyphenylene ether may be present in an amount ranging from 10 to 50 wt %. Therefore, in the resin composition, the main resin is polyolefin, rather than polyphenylene ether, resulting in insufficient heat resistance of the prepared electronic circuit substrate, and thus the prepared PCB used for high multi-layer high-speed electronic circuit has a significant heat resistance problem that delamination will occur after several harsh lead-free reflow solderings.